Assemblies for optoelectronically sensing position are well known in the prior art. These assemblies are often referred to as encoders or angle of rotation sensors. The assemblies typically include a light source, a coded element, and a plurality of photosensors. An example of such an assembly is disclosed in U.S. Pat. No. 4,621,256 (the '256 patent).
The '256 patent discloses an assembly for sensing position utilizing a light source, a coded element, and a plurality of photosensors. The coded element has a plurality of holes defining digital codes representing position. The plurality of holes is assembled in the form of multiple tracks along the coded element. One photosensor per track is utilized to receive the light passed through the holes and convert the light into electrical signals. The electrical signals are then analyzed to determine a current value of the digital codes.
Two problems are common in assemblies for optoelectronically sensing position. The first problem concerns the alignment of the coded element to the photosensors. If each track of the coded element is not properly aligned with its corresponding photosensor, then the photosensor will not detect the light passing through the holes. This results in an incorrect determination of the current value of the digital codes. The second problem concerns the build-up of contaminants in the holes of the coded element. These contaminants often result from the wear of bearing surfaces used to allow movement of the coded element. When contaminants build up on the holes of the coded element, the amount of light passing through the holes is reduced, thus resulting in the incorrect determination of the current value of the digital codes.
There remains an opportunity for an assembly that is able to operate correctly despite poor alignment of the coded element to the photosensors and build-up of contaminants on the holes of the coded element.